Carbon nanotubes have very anisotropic structures, and may be formed in various shapes such as single-walled, multi-walled and rope shapes. The carbon nanotubes may have conducting or semiconducting characteristics depending on how they are coiled, different energy gaps depending on their chirality and/or diameters, and particular quantum effects due to quasi-one-dimensional structures.
Multifunctional carbon nanotubes having particular structures and properties are widely applied to flat panel display devices, highly-integrated memory devices, secondary batteries and ultra-capacitors, which are key elements in telecommunication devices, and to hydrogen storage materials, chemical sensors, ultra-high strength/ultra-lightweight composite materials, and electrostatic removal composite materials and electronic wave blocking materials, and have potential to overcome shortcomings that conventional devices may have. Thus, various studies on such carbon nanotubes are progressing.
Particularly, in manufacturing a composite by introducing another material into a carbon nanotube, during or after the manufacturing process of the carbon nanotube, a wet-chemical method or a method of introducing metal into a carbon nanotube using supercritical fluids is known (S. Seraphin et al., Nature 362(1993), 503; P. M. Ajayan et al., Phys. Rev. Lett. 72(1994) 11 1722; S. C. Tsang et al., Nature 372 (1994) 159; X. R. Ye et al., Adv. Mater. 15(2003) 316; Z. Sun et al., Adv. Mater. 17(2005) 7 928).
However, a composite encapsulated by filling an organic molecule into a carbon nanotube has not been widely reported, and as an example of such a material, only a “peapod” has been studied (B. W. Smith et al., Nature 396(1998) 323).
Recently, it has been discussed that electronic characteristics of the carbon nanotube may be adjusted by filling an organic molecule into a carbon nanotube (J. Lu et al., Phys. Rev. Lett. 93(2004) 11 116804; V. Meunier et al., J. Chem. Phys. 123(2005) 024705), and it has been reported that an organic dopant is capillary-filled into a carbon nanotube (T. Takenobu et al., Nature Materials 2(2003) 683).
Also, characteristics of a polyacetylene chain in a carbon nanotube have been theoretically studied (G. C. McIntosh et al., Phys. Rev. B 67(2003) 125419), and a primary experiment thereon has also been conducted (J. Steinmetz et al., Curr. Appl. Phys. 7(2007) 39-41).